1. Field of the Invention
The present invention relates to a flexible boot which is made of a rubber. More particularly, the present invention is concerned with a boot which is used as a covering member for covering mechanical elements of, for example, a constant velocity joint or a steering mechanism of an automobile so as to keep dust, water and other matters away from the mechanical elements while preventing lubricant and other matters from being scattered to the outside.
2. Description of the Prior Art
In general, a flexible boot has an elastically deformable bellows which can be elongated, contracted or bent in accordance with the movement of a mechanical element. During long use in the atmosphere, minute cracks are generated in the surface of the bellows, particularly in the valleys, due to action of oxygen and ozone in the atmospheric air. Such cracks grow progressively to cause a rupture of the flexible boot at the valley of the bellows.
In order to prevent cracking in the bellows, a rubber material containing an anti-degradation agent capable of suppressing degradation effect of oxygen and ozone has been used as the material of flexible boots.
This countermeasure, however, suffers from the following problem. Namely, the anti-degradation agent contained in the rubber material tends to progressively immigrate into grease which is charged in the space inside the flexible boot, with the result that the anti-degradation agent contained in the rubber material of the flexible boot is gradually decreased to reduce resistance against oxygen and ozone, thus allowing cracking in the bellows of the boot.